1. Field of the Invention
The present invention relates to a portable monitor and warning system that is employed for detecting dangerous pressure and other ambient conditions, and providing a timely warning of such conditions. Although not limited thereto, the system is particularly suited for detecting and providing a warning of a dangerous or deteriorating cabin pressure condition in an aircraft.
2. Description of the Background Art
Throughout aviation history, there have been numerous incidents where aircraft crew members and/or passengers have been incapacitated due to hypoxia resulting from the loss of cabin pressure at high altitudes or from venturing into high altitudes in unpressurized aircraft. Hypoxia is defined as an insufficient supply of oxygen to the body""s tissues that insidiously affects the central nervous system and organs. The most compromising condition leading to hypoxia is not the immediately recognizable rapid decompression, but one where the cabin pressure is slowly being depleted because of a malfunctioning pressurization system or a slow, yet significant leak, has developed in the pressurized cabin or cockpit of an airplane. With crewmembers and passengers unaware, they may either simply fall asleep or be otherwise incapacitated.
The FAA has published requirements that define cabin pressure altitudes and time profiles that require the use of supplemental oxygen by the aircraft crew members and passengers. Cabin pressure altitude is the equivalent altitude above mean sea level at which the barometric pressure would equal the pressure in the aircraft cabin. According to the FAA""s Airman""s Information Manual, performance can seriously deteriorate within fifteen minutes at a cabin pressure altitude of 15,000 feet. The ability to take corrective and protective action is lost in 20 to 30 minutes at 18,000 feet, and in 5 to 12 minutes at 20,000 feet, which is followed soon after by unconsciousness. The FAA has thus required that supplemental oxygen be used anytime the cabin pressure altitude in civil aviation aircraft operations exceeds either 12,500 feet for 30 minutes, or 14,000 feet for any amount of time. These values for commercial aircraft operations are lower, 10,000 feet and 12,000 feet, respectively.
Though many aircraft are fitted with cabin pressurization monitoring and alerting systems, they alarm at a single altitude and do not track the 30 minute time limit in the low to high altitude corridor. Also, there are situations where the on-board system fails or is manually bypassed, thus rendering the occupants or crew totally unaware of a deteriorating or low oxygen environment. A need therefore exists for an improved monitoring system that cannot be readily bypassed, tracks time at altitude, and is not dependent on operation of other on-board systems.
The present invention addresses the foregoing concerns through provision of a cabin pressure altitude monitor and warning system that is designed to provide a warning when a detected cabin pressure altitude has reached a predetermined level. The system is preferably embodied in a portable, pager-sized device that can be carried or worn by an individual. A microprocessor calculates the pressure altitude from signals generated by a calibrated pressure transducer and a temperature sensor. The temperature sensor compensates for temperature variations in the signals generated by the pressure transducer to insure accuracy of the pressure altitude calculations.
The microprocessor is programmed to generate a warning or alarm if a cabin pressure altitude exceeding a predetermined threshold is detected. Preferably, the microprocessor executes an algorithm that generates two different types of warning or alarm outputs. A first early warning or alert when a first pressure altitude is exceeded, and a second, more serious, alarm condition when either a second, higher-pressure altitude is exceeded, or when the first pressure altitude has been exceeded for a predetermined cumulative period of time. The two altitude trigger points are based on the FAA requirements for the flight crew to use supplemental oxygen after 30 minutes of exposure to a cabin pressure altitude between 12,500 and 14,000 feet for civil aviation (between 10,000 and 12,000 feet for commercial aircraft operations), or immediately upon a cabin pressure altitude above 14,000 feet (above 12,000 feet for commercial aircraft operations). The elapsed time between the initial alert at the lower altitude trigger point, and the full alarm at the higher altitude trigger point is also considered to be an indicator of the urgency of the situation. A rather lengthy time delay of say several seconds to several minutes might indicate a relatively slowly deteriorating condition whereas an immediate transition might be indicative of a rapid decompression.
Preferably, the device provides multiple types of alarm condition indicators, including visual, audible and tactile. In the preferred embodiment, the visual output is implemented with a light emitting diode (LED) or other visual indicator that flashes when an alarm condition is triggered. A liquid crystal display (LCD) is also used to warn the user in alphanumeric text of the high cabin pressure altitude event and describe the condition of the condition influencing the alarm. It also preferably flashes a text warning to xe2x80x9cget on oxygen now!xe2x80x9d The audible output is preferably implemented with an electromechanical audio alarm, or the like, while the tactile output is preferably implemented with a mechanical vibrator. In addition, a speech synthesizer is incorporated to alert the user of the event, and to verbally describe the condition. It also preferably provides a corresponding verbal instruction to the text warning, e.g., xe2x80x9cget on oxygenxe2x80x9d. This is a preferred method from a physiological standpoint, since hearing is the last sense to be impaired at the onset of hypoxia, while cognitive ability and vision are the first to be impaired. The audio warning could be readily interfaced with the pilot""s headset through wired or wireless links to the aircraft""s intercom, avionics system, or communication or navigation radios.
In addition to being able to monitor cabin pressure altitude, the system is also preferably designed to detect gas concentrations and other ambient conditions. The system thus incorporates other sensors such as oxygen, temperature, relative humidity, carbon dioxide, carbon monoxide and ammonia sensors, to provide a more complete characterization and monitoring of the local environment. Further, since the system microprocessor can track both time and altitude, the device can also be used for indicating the pressure altitude or the rate of climb or descent in non-pressurized aircraft.